Potential for Biomass Production and Remediation by Cultivation of the Marine Model Diatom <i>Phaeodactylum tricornutum</i> in Oil Field Produced Wastewater Media

While oilfield produced water (PW) is one of the largest, unclaimed wastewater streams of the oil industry, it could potentially be used as a cultivation medium for microalgae. Microalgae could help with the remediation of this water while also delivering biomass that can be transformed into valuable byproducts such as biofuels. The coupling of these two purposes is expected to cut production costs of biofuels while aiding environmental protection. In this study, we compared the cultivation capacity of the marine model diatom <i>Phaeodactylum tricornutum</i> in media at varying salinities and in media composed of PW from two oilfields in the Central Valley of California that differed drastically in the concentration of inorganic and organic constituents. Specifically, we measured the carrying capacity of these media, the maximum growth rates of <i>P. tricornutum</i>, its cellular lipid accumulation capacity, and its capacity to remediate the most polluted PW source. Our study shows that <i>P. tricornutum</i> can successfully adjust to the tested cultivation media through processes of short-term acclimation and long-term adaptation. Furthermore, the cultivation of <i>P. tricornutum</i> in the most heavily polluted PW source led to significant increases in cell yield and improved photosynthetic capacity during the stationary phase, which could be attributed chiefly to the higher levels of nitrate present in this PW source. Chemical water analyses also demonstrated the capability of <i>P. tricornutum</i> to remediate major nutrient content and potentially harmful elements like fluorine and copper. Because <i>P. tricornutum</i> is amenable to advanced genetic engineering, which could be taken advantage of to improve its cultivation resilience and productivity in an economic setting, we propose this study as a step towards essential follow-up studies that will identify the genetic regulation behind its growth in oilfield PW media and its remediation of the PW constituents.